Alzheimer's disease (AD) is a leading cause of dementia in the elderly, affecting 5–10% of the population over the age of 65 years. See A Guide to Understanding Alzheimer's Disease and Related Disorders, edited by Jorm, New York University Press, New York (1987). AD currently affects 12 million people around the world, and is projected to affect 22 million people by 2025 and 45 million by 2050.
Alzheimer's disease is histopathologically characterized by the loss of particular groups of neurons and the appearance of two principal lesions within the brain, termed senile plaques and neurofibrillary tangles. See Brion et al., J. Neurochem. 60:1372–1382 (1993). Neurofibrillary tangles are intraneuronal accumulations of an abnormally phosphorylated form of the microtubule protein tau. Neurofibrillary tangles are most abundantly present in parts of the brain associated with memory functions, such as the hippocampus and adjacent parts of the temporal lobe. See Robbins Pathologic Basis of Disease, Cotran et al., 6th ed., W. B. Saunders Company (1999), p. 1300.
Amyloid beta peptides (Aβ) are normally secreted proteolytic products of amyloid precursor protein (APP) (Selkoe, D. J., Annu Rev Cell Biol 10:373–403 (1994)). The 42-residue form (Aβ1–42) is the principal species in senile plaques which constitute a diagnostic feature of Alzheimer's disease (AD), and is preferentially generated over shorter forms (e.g., Aβ1–40) in genetic mutations related to familial AD (Steiner, H., et al., Eur Arch Psychiatry Clin Neurosci 249:266–270 (1999)). Transgenic mice that overexpress mutant APP develop plaques accompanied by neuropathology (Guenette, S. Y., and Tanzi, R. E., Neurobiol Aging 20:201–11 (1999); van Leuven, 2000) with both effects being blocked by immunization against Aβ (Schenk, D., et al., Nature 400:173–177 (1999); Frenkel, D., et al., Proc Natl Acad Sci USA 97:11455–11459 (2000); Janus, C., et al., Biochim Biophys Acta 1502:63–75 (2000); Morgan, D., et al., Nature 408:982–85 (2000)), or by peripheral administration of antibodies against Aβ (Bard, F., et al., Nat Med 6:916–9 (2000)).
These results support the assumption that extracellular Aβ accumulations trigger pathologies and emphasize the importance of identifying links between the peptide and pathogenic processes. Infusions of Aβ into brain do not cause extensive damage (Games, D., et al., Neurobiol Aging 13:569–576 (1992); Podlisny, M. B., et al., Am J Pathol 142:17–24 (1993)), in part, because extracellular proteases prevent the injected material from assembling into plaques (Backstrom, J. R., et al., J Neurosci 16:7910–7919 (1996); Qiu, W. Q., et al., J Biol Chem 273:32730–32738 (1998); Caswell, M. D., et al., Eur J Biochem 266:509–516 (1999); Iwata, N., et al., Nature Med 6:143–150 (2000); Vekrellis, K., et al., J Neurosci 20:1657–1665 (2000)). In any event, links between extracellular Aβ and pathogenic mechanisms in mature brain remain obscure.
Brain slices in interface culture reach a surprisingly adult-like state (Stoppini, L., et al., J Neurosci Meth 37:173–182 (1991); Muller, D., et al., Dev Brain Res 71:93–100 (1993); Bahr, B. A., et al., Hippocampus 5:425–439 (1995)) and offer opportunities for in vitro studies of brain aging. Initial studies using this model found that Aβ treatment moderately enhanced cell death (Bruce, A., et al., Proc Nat Acad Sci 93:2312–2316 (1996)), while a later study found little effect of Aβ1–42 on measures of pathogenesis (Bahr, B., et al., J Comp Neuro 397:139–147 (1998)). A third study confirmed that Aβ alone did not cause pathology but in combination with transforming growth factor-β induced neuronal degeneration in field CA1 (Harris-White, M. E., et al., J Neurosci 18:10366–10374 (1998)).
The relatively weak effects of Aβ on cultured slices could reflect slow internalization and modest accumulation. Uptake of Aβ1–42 in cultured hippocampal slices occurs selectively in field CA1 (Bahr, B., et al., J Comp Neurol 397:139–147 (1998); Harris-White, M. E., et al., J Neurosci 18:10366–10374 (1998)), suggesting the existence of regionally differentiated factors that govern sequestration and regulate toxicity of the peptide. Integrins mediate internalization of bacteria and viruses (Isberg, R. R., and Tran Van Nhieu, G., Trends Microbiol 2:10–14 (1994); Nemerow, G. R., and Stewart, P. L., Microbiol Mol Biol Rev 63:725–734 (1999)) and bind Aβ via an Arg-Gly-Asp (RGD)-like sequence (Ghiso, J., et al., Biochem J 288:1053–1059 (1992); Sabo, S., et al., Neurosci Lett 184:25–28 (1995); Yamazaki, T., et al., J Neurosci 17:1004–1010 (1997)). Binding to alpha5β1 integrin, a fibronectin receptor densely expressed in hippocampus (Bahr, B., et al., Neuroreport 2:13–16 (1991); Bahr, B. and Lynch, G., Biochem J 281:137–142 (1992); Pinkstaff, J. K., et al., J Neurosci 19:1541–1556 (1999); Bi, X., et al., J Comp Neurol 435:184–193 (2001)) is required for Aβ internalization in cell lines (Matter, M. L., et al., J Cell Biol 141:1019–1030 (1998)). Moreover, the different subdivisions of hippocampus express different combinations of integrins (Pinkstaff, J. K., et al., J Neurosci 19:1541–1556 (1999)), an anatomical feature that could account for regional variations in Aβ uptake.
Integrins interact with neighboring transmembrane proteins to produce their effects on cell surface operations (Burkin, D. J., et al., J Cell Biol 143:1067–1075 (1998); Porter, J. C., and Hogg, N., Trends Cell Biol. 8:390–396 (1998)) including calcium influx (Tsao, P. W., and Mousa, S. A., J Biol Chem 270:23742–23753 (1995); Wu, X., et al., J Cell Biol 143:241–252 (1998)). NMDA receptors are calcium permeant, coupled to the actin cytoskeleton (Dunah, A. W., et al., Brain Res Mol Brain Res 79:77–87 (2000)); both calcium (Marsh, M., and McMahon, H. T., Science 285:215–220 (1999)) and the actin network (Gottlieb, T. A., et al., J Cell Biol 120:695–710 (1993)) are crucial to endocytosis. NMDA receptor function (Bahr, B. A., J Neurosci Res 59:827–832 (2000)) and maturation of synapses containing NMDA receptors (Chavis, P., and Westbrook, G., Nature 411:317–321 (2001)) have been shown to be modulated by integrins. Finally, recent studies indicate that NNMDA receptor activation can trigger clathrin-mediated internalization (Carroll, R. C., Proc Natl Acad Sci USA 96:14112–14117 (1999); Beattie, E. C., et al., Nat Neurosci 3:1291–300 (2000); Ehlers, M. D., Neuron 28:511–25 (2000)).
There has been considerable research into mechanisms underlying neurodegenerative diseases, including Alzheimer's disease. For example, many transgenic animal models of Alzheimer's disease have been developed and used in an attempt to study the mechanisms of Alzheimer's disease as well as to screen compounds that may ameliorate the conditions of Alzheimer's disease. However, many in vivo or in vitro models are unable to produce some of the important features of Alzheimer's disease, such as neurofibrillary tangles, microglia activation, lysosomal dysfunction, intracellular and/or extracellular sequestration and/or uptake and/or accumulations of amyloid, etc. Thus, there is an ongoing need to develop a model that better mimics the pathologies associated with neurodegenerative diseases including Alzheimer's disease and new ways to investigate and combat such conditions.
The present invention provides a model that better mimics some of the pathologies of neurodegenerative diseases, including Alzheimer's disease, than other models known in the art. The present invention meets these and other needs, and also provides new ways to investigate and combat such neurodegenerative conditions. Related to the present invention is U.S. application Ser. No. 09/917,789 which is incorporated by reference herein in its entirety